Scaling factor for the motion vector (actually the “shutter speed” in frames).

Speed

The vector blur could produce artifacts like streaks, lines and other.
To tackle these problems, the filter applies clamping,
which can be used to limit which pixels get blurred. The speed is set in pixel units.

Maximum Speed

The maximum threshold. The majority of artifacts are caused by pixels moving too fast.

Minimum Speed

The minimum threshold for moving pixels can separate
the hardly moving pixels from the moving ones.
Especially when the camera itself moves,
the vector mask can become the entire image.

You can make vector blur results in a little smoother by passing the Speed pass through a blur node
(but note that this can make strange results,
so it is only really appropriate for still images with lots of motion blur).